image_to_gr7.sh converts the scaled-down map image (160x80 PPM file,
generated manually using GIMP) to four Atari colors, and then
passes it to ppm_to_gr7.php which generates the final GRAPHICS 7 image
data, and Atari color palette.

Based on my work for APOD viewer for #FujiNet (server-side).

-bill!
